Posted by pyhsiclover on .
PLEASE GIVE THE ANSWER,I ALREADY INPUT TO YOUR FORMULA AND IT IS FALSE...
Is your answer 0.57?
A 15 kg, 1m wide door which has frictionless hinges is closed but unlocked. A 400 g ball hits the exact middle of the door at a velocity of 35 m/s and bounces off elastically, thereby causing the door to slowly swing open. How long in seconds does it take for the door to fully open (rotate 90 degrees)?

pyhsic question for count iblis 
Count Iblis,
The answer I posted was correct as far as I can see, the problem may well be a typo in the problem itself, e.g. a 400 gram ball slamming into the door at the speed of a speeding car is not going to "slowly" open the door.
Anyway, it's a complete waste of time to e.g. try to see if what was meant is 3.5 m/s. I would suggest forgetting about this problem and moving on to another problem, you simply say that you did the problem correctly, that the teacher made a mistake and that you demand full marks for this problem. 
pyhsic question for count iblis 
j,
iblis got the problem right. for those trying to use jiskha to cheat on the brilliant problems, there was a mistake made in the acceptable answers for this week's question.

pyhsic question for count iblis 
roger,
ibis ,I beg to differ,the door slowly open because the ball bounces back elastically,please don't be certain,when u are wrong